Warning This Web page has been archived on the Web.

Archived Content

Information identified as archived on the Web is for reference, research or recordkeeping purposes. It has not been altered or updated after the date of archiving. Web pages that are archived on the Web are not subject to the Government of Canada Web Standards, as per the Policy on Communications and Federal Identity.

Skip booklet index and go to page content

Recovery Strategy for Multi-Species at Risk in Maritime Meadows associated with Garry Oak Ecosystems in Canada (Proposed)

Species Descriptions

1.14 Coastal Scouler's catchfly Silene scouleri ssp. grandis

Assessment summary – May 2003

Common name: coastal Scouler's catchfly

Scientific name: Silene scouleri ssp. grandis

Status: Endangered Reason for designation: This is a species of highly restricted geographical occurrence in Canada with fewer than 350 plants comprising three remaining populations present on very small islands. Along with other historical population extirpations, a Vancouver Island population has recently been extirpated. These islands are located within an area of active shipping and recreational activities where invasive plants and human activities present ongoing risks.

Occurrence: British Columbia

Status history: Designated Endangered in May 2003. Assessment based on a new status report.

1.14.1 The species

Silene scouleri and its close relatives form a taxonomically difficult complex (Morton pers. comm. 2002). Most authors recognize S. scouleri Hooker ssp. grandis Hitchcock and Maguire at the subspecies or variety level.

Coastal Scouler's catchfly is an erect (15-80 cm), taprooted perennial from a branched caudex. Basal leaves form rosettes and stem leaves are opposite, reducing in size up the stem. Leaves are hairy, unstalked and have no teeth or stipules. The flowers are greenish-white to purple and form a spike. The united sepals form a prominently nerved tube. Pimply seeds are contained in dry capsules (Douglas et al. 1998b; Fairbarns and Wilkinson 2003).

1.14.2 Distribution

Coastal Scouler's catchfly occurs in a small area of southeastern Vancouver Island and nearby areas of Washington (Figure 5). The northern populations are disjunct by about 550 km from the main range of the species, along coastal areas from southern Oregon to the San Francisco Basin.

In Canada, coastal Scouler's catchfly is restricted to two small islands near Victoria, BC. The historical extent of occurrence encompassed approximately 600 km² although the current extent of occurrence is about 0.6 km². The COSEWIC status report (2002) estimates the area of occupancy to be 1.58 ha yet subsequent surveys revise this figure to 2.0 ha (Fairbarns pers. obs. 2004).

Coastal Scouler's catchfly has not been ranked globally or in the states of California, Oregon and Washington (NatureServe 2004). The species is absent from central and southern Washington State as well as northern and central Oregon. This raises the possibility that the Canadian populations (together with nearby populations in north-central Washington State) may have become genetically distinct from populations in the main range of the species.

1.14.3 Population and distribution trend

The COSEWIC status report describes two extant populations and at least six further populations that have become extirpated although there may have been up to four further populations. (Table 13).

The COSEWIC status report estimated a total population size of between 278 and 328 mature (flowering) plants. Surveys in 2004 revealed the existence of a further 18 flowering plants on Trial Island. The total past Canadian population is unlikely to have exceeded 5,000 individuals.

Figure 5. Global and Canadian distribution of coastal Scouler's catchfly
(Global distribution on left; Canadian distribution on right; triangles show extirpated populations and stars show extant populations)
Figure 5. Global and Canadian distribution of coastal Scouler's catchfly (Global distribution on left; Canadian distribution on right; triangles show extirpated populations and stars show extant populations)

1.14.4 Biotic and abiotic features of habitat

The habitat ofcoastal Scouler's catchfly consists of mesic maritime meadows. The COSEWIC status report provides information on ecosystem structure supplemented by recent vegetation sampling (Fairbarns pers. obs. 2004). Suitable meadows are less than 30 m above sea level although the Mount Tzuhalem population occurred at about 250 m and the elevation of the extirpated Mount Douglas population was also higher. The meadow soils are moist throughout the winter months but dry almost to the permanent wilting point by late summer. Most plants are rooted in soil over 15 cm deep, and those plants that do occur on shallow soils wilt before flowering (except in the very wet summers). The sites have never been ploughed or hayed, but some have been lightly grazed by livestock and most probably burned in the past.

Trees are generally absent due to the wind exposure, salt spray and the droughty nature of the shallow soils. There was a very open canopy of Garry oak (Quercus garryana) at the Mount Tzuhalem site. Native shrubs are often sparse or absent although snowberry (Symphoricarpos albus) and Nootka rose (Rosa nutkana) are sometimes present. These two shrub species often form dense thickets at the edge of populations of coastal Scouler's catchfly and may advance into the populations in moist years, presenting a threat to the species. Wildfires and First Nations burning may have formerly constrained the advance of these low shrub thickets. Alien, invasive shrubs such as Scotch broom (Cytisus scoparius) and gorse (Ulex europaeus) (and to a lesser extent spurge laurel [Daphne laureola], English ivy [Hedera helix] and Himalayan blackberry [Rubus discolor]) are sometimes abundant and will probably invade all locations of coastal Scouler's catchfly in the absence of continuing control activities.

A mix of native and introduced species typically dominates the herb layer. The leading native species are forbs (strawberry [Fragaria spp.], bracken fern [Pteridium aquilinum], white-top aster [Sericocarpus rigidus], field chickweed [Cerastium arvense], yarrow [Achillaea millefolium], woolly eriophyllum [Eriophyllum lanatum], Puget Sound gumweed [Grindelia integrifolia], barestem desert-parsely [Lomatium nudicaule]), although native grasses (tufted hairgrass [Deschampsia cespitosa], blue wildrye [Elymus glaucus], red fescue [Festuca rubra]) are also present at some locations. Common camas (Camassia quamash) and broad leaved shootingstar [Dodecatheon hendersonii] are abundant in the spring at some locations. Introduced grasses (common velvetgrass [Holcus lanatus], Kentucky bluegrass [Poa pratensis], sweet vernalgrass [Anthoxanthum odoratum], hedgehog dogtail [Cynosurus echinatus]) are usually more abundant than introduced forbs (hairy cat's ear [Hypochaeris radicata], sheep sorrel [Rumex acetosella], ribwort plantain [Plantago lanceolata], common vetch [Vicia sativa]).

Table 13. Population information for coastal Scouler's catchfly in Canada
PopulationLand TenureData from Status ReportSubsequent Data
DateObserver# PlantsDateObserver# Plants
Trial IslandPopulation is largely restricted to a parcel of provincial land leased to a radio-communications corporation. A small portion of the population (< five plants) may extend slightly into adjoining provincial ecological reserve but this can only be determined by legal survey2001Fairbarns52004Fairbarns23
Little Trial IslandProvincial land designated as an ecological reserveNot reported2004Fairbarns14
Alpha IsletProvincial land designated as an ecological reserve2001Fairbarns6732003Fairbarns370-500
Mt. TzuhalemProvincial land designated as an ecological reserveExtirpatedno subsequent data
Ten Mile PointUnknown
Uplands ParkMunicipality of Oak Bay (designated as an urban park)
Beacon HillCity of Victoria (designated as park)
Bare IslandIndian Reserve
Cedar HillMunicipality of Saanich (designated as park)
Griffin IslandProvincial land designated as an ecological reserveFalse report (likely collected from Alpha Islet population)
'near Victoria'UnknownImprecise locations, may be the same as populations listed above
Burnside Dist.Unknown
Oak BayUnknown

1.14.5 Annual cycle

Information in the COSEWIC status report has been updated by subsequent field studies of plants on Trial island (Fairbarns in. prep. e.).

Established plants send out new shoots in July, August and September after the summer drought is broken. The shoots grow slowly during the winter but in May and June reproductive shoots elongate. Some of the tall shoots wilt and die back during the summer drought in July and August. Less stressed tall shoots develop flower buds, which begin to swell in late June and flower in July or early August. Most plants have ceased flowering by late August although plants on moister microsites may continue to develop flowers into September or October. Late forming flowers fail to produce viable fruit. Mature fruit on early flowers begin to dehisce in late August. Seeds gradually sift out of the dehisced capsules as shoots are shaken in the wind and late-maturing capsules may continue to shed seed well into November. Most dead shoots remain upright long after all seeds have been dispersed.

1.14.6 Biologically limiting factors

Germination occurs in March or April, when dense clusters of seedlings are sometimes found near the base of plants that bore seed in the previous year. Seedling mortality is high, with many seedlings wilting during brief dry periods when the upper soil layers dry out. Survivors grow slowly and do not flower in their first year. It is not clear how long plants take to flower in the wild but even in well-watered gardens most plants do not flower until they are three years old.

Many shoots fail to elongate in any given year, and those that do often succumb to drought-induced wilt before flowers are produced. Reproductive shoots that survive until the summer drought is broken often fail to produce viable seed before cool autumn weather arrives and development ceases. Immature capsules rot during the winter. The potential for recovery of coastal Scouler's catchfly is limited by the failure of some populations to produce viable seed before growth ends with cool fall weather.